


pari passu

by celegant



Category: NCT (Band)
Genre: Accidental Bonding, Alternate Universe - Harry Potter Setting, Alternate Universe - Hogwarts, Enemies to Friends to Lovers, Gryffindor!Donghyuck, M/M, Potions Accident, ft. room of requirement shenanigans, slytherin!mark
Language: English
Status: In-Progress
Published: 2020-05-07
Updated: 2020-08-24
Packaged: 2021-03-03 01:40:39
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 6,784
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24036787
Author URL: https://archiveofourown.org/users/celegant/pseuds/celegant
Summary: It was an empathy potion. Sort of.One that was designed to let Aurors temporarily utilize legilimency and communicate telepathically on the field, allowing partners to monitor each other's emotions and status over long distances.'Three drops every six hours to maintain the connection, it is only to be used for the most covert missions. This potion is advised to be ingested only by individuals that share profound trust with one another, due to the intrusive nature of the magic.’(or: one Potions mishap later, and all of Mark's carefully built up walls come tumbling down. But then again, it was never really an issue for someone like Donghyuck anyway.)
Relationships: Lee Donghyuck | Haechan/Mark Lee
Comments: 56
Kudos: 347





	1. una anima

**Author's Note:**

> a little prologue to kick off this project! and as always, a thank you to julia for being my lovely beta and for listening to me ramble about this au ♡

**Notes for the Chapter:**

> Edited on August 24, 2020.
> 
> I'd actually rewritten some parts of chapter one to fit the tone for the rest of the fic, so please keep that in mind! :>

The one downside to having Head Boy duties so early in the morning is that Mark usually gets the short end of the stick when it comes to their morning Potions class. He’s usually never this late, but he manages to make it into the room with only a couple minutes to spare.

Still trying to catch his breath from rushing down the halls, Mark pauses by the door, scanning the room for any unoccupied seats. He spies Jaemin already sitting next to Jeno at their usual table, his bright shock of hair almost like a beacon by the far end of the classroom.

At Mark's withering glare, he sees his fellow Slytherin throw him a small, sly grin, almost Cheshire-like as he nods at Mark in greeting. Jaemin looks over to his side, eyes flitting briefly over to Jeno before he turns back to Mark, shrugging helplessly at the fact that Mark's usual seat seems to have been taken.

Mark suppresses a tired sigh.

It was Jaemin's fault that Mark was running late in the first place. If he hadn't kept the Slytherin prefects out all night during their patrols—after reports had come in of finding individuals in compromising situations in the dark alcoves of the third floor—then Mark wouldn't have woken up so late. He wouldn't have missed the morning rounds, and he wouldn't be standing there, at the entrance to the classroom, pitifully partner-less for today's assignment.

Mark spots an empty table just behind them, and goes to move towards it when another boy comes barreling down into him. He reaches out on instinct, steadying the other boy by the arm as he tips forward.

"Sorry, sorry, that was my bad."

Despite the boy's breathlessness, it was a voice that was entirely too familiar. Lee Donghyuck.

Mark's hand recoils as if he'd been burned, the action almost unconscious, and Donghyuck looks up, his apologetic smile quickly turning into a scowl at the sight of his supposed savior.

"Nice of you to join us, Mister Lee and Mister Lee," the professor calls out from the front of the room. "And now that our final pair has arrived, if you could both please grab your seats, we can get started on today's assignment."

Mark blanches at the thought of partnering with Donghyuck, and he knows the sentiment is returned when he feels Donghyuck stiffen next to him. Swallowing his protests, Mark moves to take his seat at the empty table, making sure to keep his distance from the Gryffindor next to him as Donghyuck slides onto his own seat.

He sees Jaemin's shoulders shaking in mirth in front of him, and Jeno turns around to meet his eyes with an apologetic expression, head tipping towards Jaemin as he mouths a quick ‘ _sorry_ ’ in Mark's direction.

Mark shakes his head once in response, and Jeno dutifully turns back to face the front of the room. Jaemin is _absolutely_ going to be hearing an earful from him when they get back to the dorms.

He turns his gaze to the chalkboard in front of the room, the monotonous drone of their professor's voice going in through one ear and out the other. He's going through the steps of today's assignment, Mark observes, and he tries to stifle a short yawn behind the back of his hand as the fatigue from last night catches up to him.

Mark frowns though, as he takes in the length of the recipe for today's brew. Potions was never particularly his strong suit, not compared to other subjects like Charms or Herbology. Hell, he was even better at _Divination_ than he was at Potions.

As much of a perfectionist as Mark prided himself on being, he never quite got the intricacies of potion-making. Unfortunately, his disastrous abilities in the kitchen seemed to translate to the cauldron—he was always more of a ‘ _go with your gut_ ’ kind of guy, as opposed to exacts and precise measurements.

After years of botched potion after botched potion, he'd eventually learned to just rely on Jaemin to make sure he doesn't fuck up their assignments.

At least, that was his _usual_ plan.

He glares at the back of Jaemin's head one last time, before chancing a glance to the side, seeing Donghyuck rifling through their text to find the pages for their assigned potion. Loathe as he is to admit it, he knows that Donghyuck was a natural at this—Potions was one of his favorite subjects after all.

 _(It always has been_ , the voice in the back of his head unhelpfully supplies. Mark chooses to ignore it.)

Mark lets out another soft sigh. Their potion would probably be fine, as long as they work together.

(The operative word here being _together_.)

☾ ☼ ☽

It was an empathy potion. Sort of.

One that was designed to let Aurors temporarily utilize legilimency and communicate telepathically on the field, allowing partners to monitor each other's emotions and status over long distances.

_'Three drops every six hours to maintain the connection, it is only to be used for the most covert missions. This potion is advised to be ingested only by individuals that share profound trust with one another, due to the intrusive nature of the magic.’_

They weren’t actually going to be taking the potion, not while they were still students. They were just meant to brew it and be graded on potency. Still, the fact remains.

How ironic.

“Stop staring at me.”

Annoyance flashes through Mark as he feels Donghyuck’s gaze bore into the side of his head. “Pay attention to your own hands, Donghyuck.”

They were about twenty minutes into the brewing process, and Mark had been tasked with keeping an eye on the cauldron while Donghyuck prepared the ingredients.

He knew he was given cauldron duty because he couldn’t be trusted to differentiate between powdered Aconite and all the other faintly shimmering powders in front of them. Still, the scrutinizing glare Donghyuck was directing at him was starting to become unnerving.

Mark hears Donghyuck scoff, disdain dripping from his voice. "You're stirring it wrong."

He looks down at the cauldron bubbling in front of him, the sickly green shade almost fluorescent. His hand continued to stir clockwise, counting six turns before going the other direction.

Eyebrows furrowed, Mark looks back up with a frown. “What do you mean? The book says to go clockwise—”

"No, wait,” Donghyuck's hand reaches out to stop him. “You're supposed to go clockwise _three_ times, then counterclockwise once, then back the other way."

Mark rolls his eyes, continuing to haphazardly stir the simmering liquid. “I really don’t think it _matters—”_

He reaches for the next ingredient, what looks to Mark like a handful of crushed herbs, but Donghyuck smacks his hand aside. The pained yelp and subsequent exclamation of _‘hey!’_ from Mark is primly ignored.

“Are you trying to fuck this up for us on purpose?” Donghyuck asks, exasperatedly. “You were about to add in _Asphodel,_ Mark. Are you actively trying to kill us?”

Cheeks reddening at his mistake, Mark glares back at him. He reaches for the other pile of leafy green plants, tossing them into the mixture with a bit more force than was necessary. “There. Are you happy now?”

Donghyuck’s smirk was insufferable. “It’s a wonder how you even passed your OWLs with these kinds of skills. I think maybe you should just quit while you’re ahead.”

Mark jumps then, feeling a sharp prick near the back of his head. He looks up to Donghyuck grinning cheekily up at him, a strand of Mark’s dark hair pinched in between his fingers.

“What the hell is your problem?”

Mark hears Donghyuck huff beside him. “We need it for the potion, calm down. The recipe calls for both strands of our hair to establish the link.”

He plucks a strand of his own honey-brown hair, letting them both fall into the pot.

“What even is the point to this? It’s not like we’re gonna drink it anyway,” Mark mumbles, rubbing the sting away. He looks back down, watching as the potion shifts from green to a pale yellow. Reaching over for the open book, he skims over the next steps before pausing at the very bottom text.

_‘Caution is advised when handling frozen Ashwinder Eggs, as they should never be added to the concoction prior to the users’ strands of hair. Please alert your nearest instructor/supervisor if the colour deviates from the green—’_

Mark’s head whips up, quickly scanning their table for the Ashwinder Eggs, but finding none.

“Donghyuck, when did you add the Ashwinder Eggs?” he asks, a frantic edge to his voice.

The other boy lets out a confused noise, “What do you mean? I haven’t added them yet—”

Mark hears it then, a sharp sizzling noise. He may not be an expert at this, but he knows that sizzling is never a good sign. Both their heads turn to the potion in horror as the rolling boil becomes turbulent, a dark plume of smoke starting to erupt from the cauldron.

Donghyuck’s head whips over to Mark, accusing. “What did you _do?”_

“I didn’t do anything—”

Mark doesn’t get to finish his sentence, their potion exploding in a sudden flurry of yellow splatter. The potion smells sweet, almost cloyingly so. It’s warm too, a tingling trace beginning on parts of his skin that had come into contact with the liquid.

It takes them a second then, just blinking at each other while covered in the questionable concoction. Mark mutters a quick _Scourgify_ and it’s gone in a flash, Donghyuck following suit with a renewed scowl on his face.

“Nice going, Mark, now we gotta start over.”

Mark looks at him in disbelief. He can’t seriously be putting the blame on him right now.

“How is this my fault?” he asks, voice incredulous.

“Well, who _else_ could it have been?”

“Yours, obviously—”

“Okay, boys, enough!” Their professor interrupts, walking over and eyeing the mess around the table. “I want the both of you up at the Hospital Wing right this instant.” His eyes rake over the now half-empty cauldron before frowning. “And afterward, you will come back tomorrow evening to re-do the assignment, do I make myself clear?”

“Yes, Professor,” they say in unison, properly admonished.

With their professor’s back turned to them, Donghyuck sneaks one last look at Mark, glaring at him and sticking his tongue out childishly. Mark could only roll his eyes once more, shoulders dropping at the thought of spending another afternoon with Donghyuck.

All alone.

Mark sighs. _This is all Jaemin’s fault._

☾ ☼ ☽

They get the all-clear from the healers, nothing out of the ordinary as far as they were concerned. No physical symptoms, and it didn’t seem like either Mark nor Donghyuck could hear each other’s thoughts. So, it seems like the potion didn’t even work.

They were sent back to class with little more than a pat on the back and a bit of chocolate for the road.

Mark spends the rest of the day trying to forget about the incident. Luckily, he doesn’t have any more classes with Donghyuck—he doesn’t know if he could deal with seeing more of him today. But still, his mood gets progressively more irritable as his classes fly by, both Jaemin and Lucas periodically sending him concerned glances.

By the time dinner rolls around, and Mark takes his seat at the Slytherin tables in the Great Hall, he’s got a full-on headache pounding in between his eyes. The hall is loud, like everything’s being amplified right in his ears. His dinner goes mostly untouched, stomach rolling uncomfortably at the thought of eating anything right now.

“Mark, hey, are you okay? You don’t look so hot, man,” Lucas points out, and it takes Mark a second to register the fact that the guy had been talking to _him._ Mark looks up, bleary eyes blinking up at the taller boy. Lucas always did stand out a bit too much, both for his bigger-than-life personality, and for the fact that he was a Hufflepuff that spent most of his time at the Slytherin tables.

“Mark?”

“It’s nothing,” he says, a little too quickly. He didn’t realize how much he was starting to zone out. Mark brushes Lucas’ questioning look away with a wave of his hand. “It’s been a long day, and I didn’t get much sleep last night, that’s all.”

“No, but Lucas is right though,” Jaemin pipes up from across from him. “You _do_ kind of look like shit.”

Mark levels him with a pointed look. “Gee, thanks,” he says, with as much sarcasm as his tired brain could muster. “Wonder whose fault that is.”

Jaemin just smiles at him again, all teeth, a picture-perfect still of innocence. “Well, I can think of a few reasons that’d keep you up at night.”

Like a gravitational pull, he feels another set of eyes on him, prompting Mark to look past Jaemin and across the hall towards the Gryffindor table. Donghyuck’s glaring at him again—when does he not?—and he finds himself mirroring the expression. He mouths a quick, _‘what?’_ in Donghyuck’s direction, only to watch as the other boy shakes his head, getting up to leave the Great Hall entirely.

“Hello? Earth to Mark?” Jaemin snaps his fingers in front of Mark’s eyes, grabbing his attention back from where his eyes had trailed after Donghyuck leaving through the doors.

“Sorry,” Mark apologizes. “What were you saying?”

Jaemin snorts. “Nevermind. It’s nothing,” he says, affectionately petting the back of Mark’s head. “You don’t have to worry your pretty little head over it.”

Mark hears Lucas chuckling beside him, and he knows he’s missing out on something. The pounding in his head is starting to make itself known again, so he shoves it aside for now. He rubs at his temples one more time before he gets up as well, grabbing his bag to head back into the dungeons.

Before he leaves the table, he turns back to the two boys in front of him. “Yukhei, can you and Jeno cover my rounds for tonight? I think I’m gonna call it early tonight.” Mark pauses then, remembering his duties as Head Boy. “But wake me up if something comes up, okay? I’ll come right back up.”

Lucas shakes his head. “You need your rest, Mark. You haven’t taken a proper break in like, forever.” He grins up at him, and Mark can’t help but feel grateful. “We got this, don’t worry about it. Just feel better, alright?”

“And I’ll let Jeno know,” Jaemin adds. “Still want me to wake you up in the morning?”

Mark nods at Jaemin, and smiles down at the both of them. “Thanks, guys. I owe you both one.”

He takes his time walking back down to the Slytherin dorms, the uneasy feeling in his chest not having dissipated in the least. Mark thinks about Donghyuck’s hasty retreat from dinner, and wonders if this is the failed potion talking—some late after-effect the healers didn’t catch.

He brushes the thoughts away. No use worrying over it right now, he can always visit the Hospital Wing in the morning if he doesn’t feel any better. For now, his only priority is making it to the dorms in one piece so he can pass out in his bed.

The Slytherin common room is mostly empty, save for a group of stragglers studying quietly by the fireplace. They greet Mark as he passes through, making a beeline for the boys' dormitory, but he only manages a clipped nod and a strained smile in return.

He enters the dorms and breathes out a sigh of relief at the silence that greets him. Mark makes his way over to his bed, hesitating for a second before settling in front of his trunk. He rummages around, feeling for the small rectangular box hidden under the layers of clothing. He brings it out with shaking hands, taking one last glimpse around the room to make sure no one was around.

Mark opens the box, counting the small purple tinctures lined up neatly within. He takes one out, pulling the stopper and downing it all in one go, wincing a bit at the medicinal taste. He doesn't think he'll ever get used to it, really, despite the number of times he's had to take it.

He places the box back inside his trunk, locking it back up. Jaemin tends to snoop around some days, and Mark knows he'd throw a fit if he found out that he was back on the sleeping draughts.

Drawing his curtains closed, Mark murmurs a quick silencing spell around bed and succumbs to the pull of another dreamless sleep.

☾ ☼ ☽

Mark wakes up to the sound of obnoxious chatter.

_—’m gonna be so late—_

An endless litany of unintelligible words fill his ears, and he sits up, groggily blinking up at the darkness from his closed blinds. He whispers a quick _Tempus_ , irritation running through him at the sight of 6:30 am.

 _Why is everyone making so much noise this early in the goddamn morning_? Mark thinks.

— _didn’t those idiots wake me up—_

He pauses, squinting at the familiarity of the sound of the voice. It’s familiar, but distorted enough that Mark couldn’t quite place who it was.

_—am I so tired today? Ugh—_

His skin starts to crawl. Something’s wrong. He’s hearing voices, but it doesn’t sound like there’s much movement outside of his bed. Mark draws his blinds open, freezing at the sight of Jaemin’s sleeping form splayed out in the bed next to him.

He looks around the rest of the room, everyone’s still asleep, curtains closed. Mark doesn’t _see_ anyone talking or even so much as making a single sound.

_—the fuck? Oh my god what—_

The voice inside Mark’s head sounds frazzled, and he feels a sense of hysteria rising within him. God, Mark is really really hoping what he thinks is happening isn’t _actually happening._

_—I’m going… fucking kill him—_

Mark recognizes the voice now, desperately wishing that this was all just a sick dream and that he could go back to bed so he could wake up for real.

_Mark Lee._

He sighs, then, one last time as he resigns himself to the fact that _this_ is his fucking life.

_Donghyuck?_

**Notes for the Chapter:**

> [cc](https://curiouscat.me/dhyuckiees) | [twitter](https://twitter.com/dhyuckIees)
> 
> feel free to let me know what you think!! I'm super excited to see where this'll go *v*


	2. ab initio

Contrary to popular belief, they haven't always been at odds with each other.

Actually, now that Mark takes a second to let himself reminisce, there used to be a time when they were almost damn near inseparable.

Mark and Donghyuck, Donghyuck and Mark. If you had asked the other students back then, back before that fateful summer before the start of their fourth year, they would've told you that one couldn't be found without the other trailing closely behind.

They'd made quite the name for themselves together, even back when they were still bright-eyed first years—such a peculiar relationship between a Slytherin and a Gryffindor, and between a pureblood and a muggleborn, no less.

But Mark didn't care, not at the time. All that mattered was that he'd found a friend in the young Gryffindor, so different from all the other pureblooded children he'd grown up with, so curious about magic and so full of life that Mark couldn't have looked away, even if he'd tried.

Mark remembers sneaking into each other's dorms past curfew, he remembers the long hours spent hiding under the blankets, one ear out for the patrolling prefects as they talked about their homes, their families, their dreams. He remembers all the petty squabbles, all of the fond but exasperated looks they'd get from Mark's brother, and all of the reconciliatory sweets passed across the table after a particularly nasty fight.

They had been friends once— _best_ friends, even. Three years of friendship ruined seemingly overnight.

But Mark had made a choice. And it wouldn't be fair to either of them if he lets himself regret it.

It's been years now though, and whatever lingering sentiment he and Donghyuck might have felt for each other is long gone, nothing left between them other than bitter animosity and a painful reminder of a friendship that could have been.

☾ ☼ ☽

— _can't fucking **believe**_ —

Mark sighs. It's a sad, endlessly tired sound.

— _missing practice to deal with this bullshit_ —

The constant rhythm of shoes pacing back and forth against the concrete floor. Eyes squeezing tightly shut, Mark's shoulders slump when he hears a frustrated huff from the other side of the room.

— _guy has **some** fucking nerve to_—

He hears a whispered expletive, one that isn't just in his head this time, and not for the first time that morning does Mark wonder what on earth he did wrong in a past life to deserve this. He doesn't have to open his eyes to know he's being glared at—can feel the heat of the gaze piercing through the side of his head.

Another huff. The pacing continues.

— _hate him hate him hate him so much stubborn prick_ —

"Can you _please—_ for one fucking second!" Mark hisses from across the ward. "Can you please stop thinking so goddamn loudly?"

He's perched atop of one of the hospital wing's beds, both elbows on his knees as he sits cross-legged, the stiff, scratchy white beddings crinkling noisily as he shifts in his seat. Mark drops his head into his hands, fingers rubbing circles against his temple in a poor attempt to stave off the worsening of his headache.

"Well, excuse me for being _a little upset_ that you put us in this mess in the first place," Donghyuck spits back, turning around just in time to see Mark flop backwards onto the bed. "Your thoughts aren't exactly sunshine and rainbows either, asshole."

"Can you at least stop moving?" Mark grunts, pressing the heels of his palms into his eyes. "Your pacing is making all of this worse." He sighs one more time, before sitting back up to return Donghyuck's glare with a sharp one of his own. "Also, how the fuck are you even moving at all? Don't you have a headache too?"

"Of course, I have a headache," Donghyuck scoffs. "How could I not when all I'm constantly hearing in my head is you telling me to shut up and," Donghyuck raises his voice then, in a bad impression of what he assumes to be Mark's voice. " _'Please, please, please let this be just some sort of fucked up dream.'_ " His frown deepens, almost a sneer as he regards Mark in front of him. "Well, I've got some news for you, Golden Boy. This isn't a dream. This is a very fucked up, very _real_ nightmare."

"As if I didn't already know that," Mark mutters. "It's _you_ I have stuck in my head, it couldn't have been anything other than a nightmare to begin with."

Donghyuck opens his mouth, no doubt ready to fire off another scathing retort, but is interrupted by the sound of the hospital wing doors flying open, the rushing footsteps making both their heads turn to see their Potions professor trailing behind a healer—dressed in the signature green of mediwizard robes, although this particular healer isn't one that Mark has ever met before.

The healer—Kun, as he would later introduce himself—steps forward wordlessly, wand raised in Mark's direction as it begins to emit a soft green glow. He runs the wand over Mark’s body from top to bottom and then back up, pausing for a second by his chest before focusing around his temple. Eventually, the light fades and he moves to do the same to Donghyuck, his brows furrowed in concentration as he takes in the readings that neither of them can see.

When he finishes examining Donghyuck's head as well, he steps back, eyes flicking back and forth between the two of them before beckoning their professor over. Kun turns to him first, a concerned frown on his face as he asks, "It was an empathy potion, you said?"

Their professor nods. "Yes. It was supposed to be a weaker version of the original potion, and should've worn off about a few hours after ingestion. The students weren't supposed to actually take it though, and these two were only exposed to the potion when it exploded all over them."

Kun hums, a thoughtful look on his face. "It must've been aerosolized and ingested when they breathed it in, which explains the delayed effect." His frown deepens, turning back to the boys in question. "Although, it still doesn't explain why it's lasted this long. Or why it exploded in the first place."

Mark and Donghyuck exchange a look, and they didn't need the telepathic connection to figure out what the other was thinking about.

"Could it have been the Ashwinder Eggs?" Mark asks, apprehension clear in his voice. “They were missing when the potion exploded.”

He watches as realization dawns on their professor's face, eyebrows raising in surprise before lowering back to a furrow, expression darkening as he realizes what went wrong. Mark suppresses a wince, as their professor's face reddens, no doubt ready to go off on them for not paying attention in class.

"Boys, I explicitly told you _not_ to add the Ashwinder Eggs until _after_ —"

“But it wasn’t—”

“It was all his fault—”

"Be that as it may," Kun interrupts the three of them, hands raised in a placating manner. "What's done is done. The potion's already taken effect, and what we need to focus on right now damage control **.** We'll need to look into why it hasn't worn off and how to mitigate the symptoms in the meantime. **"**

"Professor, surely there's precedent for something like this? A counter-potion, an antidote? _Anything_?" Donghyuck asks, a bit of a desperate edge peeking through his voice, fingers clenched tightly by his sides, the soft leather of his gloves crinkling under the pressure.

He's still in his quidditch practice uniform, Mark belatedly notices.

"There have been cases in the past where the improper use of the eggs has resulted in similar explosions, but most of those cases resolved themselves within the usual timeframe for the potion. I will have to look further into whether there have been any cases of prolonged telepathy..." Their professor trails off, and a moment passes in silence as he loses himself in his thoughts before he looks up abruptly and shakes his head. "I will have to look into the records,” he repeats. “But it will take some time."

_Oh, fuck no—_

He hears Donghyuck let out a strangled noise from his side of the room. " _Time_? How long are we going to be stuck like this?"

— _no no no need him out immediately_ —

The expression on their professor's face turns apologetic, the uncertainty in his eyes belaying no comfort as he turns his attention over to Donghyuck.

"I'm afraid... I can't give you an answer right now, Mister Lee. Not until we figure out exactly what went wrong. Your old cauldron is still in the classroom, thankfully, so we'll be able to run some tests on its composition post-haste."

Mark can feel Donghyuck's rising sense of panic mirrored within himself, and not just because of the link, so he turns to Kun instead. "Isn't there some way to block the bond? It's meant to be based off of legilimency, right? Isn't there anything we can take that can mimic occlumency in the same way?"

But Kun just shakes his head at the request. "We can't give you anything else that might confound the effects of the current potion, unfortunately." He pauses for a moment in consideration. "Although, spells are a different matter. Neither of you would happen to be trained Occlumens users, would you?"

— _fuck_.

They both shake their heads. It's one of the biggest downsides to the link, Mark realizes, the echo chamber of emotions bouncing back and forth between them, amplifying the distress and hopelessness currently festering in their heads.

"Then we will have to arrange for lessons," Kun continues, pausing for a beat as he studies both of the boys with a small frown. "Although, the problem is that we don't have anyone with the expertise currently on faculty, at least not that I know of. We may have to bring in a certified Auror for a case like this."

"Oh, I can make arrangements for that while I report to the headmaster," their professor chimes in, nodding once before preparing to leave. "Which reminds me that I should probably go do so right now. I shall leave you both in Healer Kun's hands to finish the rest of the diagnosis, but please don't forget to report to my office after dinner." He ignores the twin groans of protest. "Regardless of your current situation, you two still need to re-do the potion to pass this assignment."

— _ugh can this **get** any worse_—

 _My sentiments exactly_ , Mark thinks, the both of them in agreement for once. They make their promises to be there for the assignment and they watch as their professor bids them a quick farewell, the three of them silent until the doors to the hospital wing swing back closed.

"So," Kun turns back to them, Accio-ing a chair for him to sit on in the middle of the two beds, as well as a piece of parchment and a self-writing quill, the both of which stay floating a few inches away from him. "I'm going to ask you both a few questions, just so I can get a better idea of what this link is like, and how strong it's holding up. Your physical readings seem to be normal for the most part, save for the headaches, correct?"

They both nod an affirmative, Mark's back sitting up straighter at the prospect of an oncoming inquisition. He sees Donghyuck take a proper seat on his bed, fingers fiddling together in his lap with a displeased expression on his face.

"First off, how much of each other's thoughts can you actually hear?"

— _too fucking much_ —

"Just snippets, mostly," Mark answers dutifully, shooting Donghyuck a pointed look when the other scowls. "Phrases, parts of a couple sentences here and there, but it's not like we can talk to each other in our heads."

— _just wish you could I'm sure_ —

Kun turns to Donghyuck for confirmation and the Gryffindor nods. "It's about the same for me," he says. "But the phrases are getting longer though? It was worse this morning, I could only pick up on a couple of words, and it wasn't until he woke up that I started hearing anything, I think."

The quill above Kun scribbles furiously, transcribing the boys' words and jotting down the relevant notes for him to review later on. Kun crosses his legs, leaning forward to rest an elbow on his knee as he rests his chin on the palm of his hand. There's a curious glint in his eyes as he looks between the pair, like him and Donghyuck were some rather interesting test subjects, a rare chance at studying something so peculiar.

"So it seems the bond is still settling in then," Kun murmurs absently, more to himself than anything else. "That makes sense, because the potion was botched. It was designed for proper communication over long distances though, so you should both expect to be able to talk to each other mentally once the link is fully formed."

Mark chooses to ignore Donghyuck's pained groan. His temple throbs one more time.

"And the headaches?" Mark asks. "How long are these going to last?" He winces as the pounding pressure behind his eyes gets stronger. "It feels like my head's being split open, even when I can't hear him."

Kun's brows furrow at Mark's question, and he stands up once more, wand raised to Mark's head, but this time with a soft blue light instead of green. It's warm this time, Mark muses, the light pulsing gently as Kun moves the wand from one temple to the other.

Mark watches as Kun frowns once more, eyes fixated on his wand as the light changes from the pale blue to a bright orange, flashing slowly for a handful of seconds before fading back to blue.

"Donghyuck," Kun calls out, before moving over to him. "Do you mind?" he asks, raising his wand as he did with Mark. Donghyuck shakes his head minutely as Kun examines him, though he sits up straighter when the blue light shifts to yellow instead of the orange that they saw with Mark.

Kun lowers his wand, a contemplative look on his face as he regards Donghyuck in front of him. "On a scale of one to ten, how bad would you say your headache is right now?"

"A five, probably?" Donghyuck answers. "Like, there's a bit of pressure, but it doesn't feel any different from any other headache? Why?"

Kun just hums in lieu of an answer. "Mark?"

"Eight?" Mark says, looking up from where he'd been cradling his head in his hands after Kun had gone over to Donghyuck. "No, wait. Closer to a nine. It gets worse when I focus on something moving, I think."

"I see..." Kun trails off. "As far as I'm aware, the potion shouldn't have any negative side effects. Not ones that induce any headaches, at least."

"What's wrong with us then?" Donghyuck asks.

"It's just a theory for now," Kun starts. "But judging from the tests I just ran, I think what might be happening right now is that it's just _Mark_ that's actually experiencing these symptoms," he turns to Donghyuck then, eyes wary as he says, "but because of the bond, it's spilling over to you, Donghyuck, and you end up feeling whatever he's feeling—albeit, not as severely."

Irritation rips through Mark, suddenly and viciously, and the hint of indignation that accompanies it clues him into the fact that these feelings may not be his own. He looks towards Donghyuck and catches the tail end of his surprised expression, eyes wide and eyebrows raised at Kun's words, before it falls back into the scowl that Mark's come to know so well.

"I'm afraid I'm going to have to ask you both to come in for regular check-ups," Kun continues, settling back into his chair. "At least until the bond settles, and we can rule out any other anomalies. It'd be good for me to monitor these headaches too, if they persist."

Kun flicks his wand towards the parchment still floating in the air, two smaller pieces ripping off of the scroll as his quill makes quick work of signing them.

"I'd like you both to pass by my office first thing in the morning for the next two weeks," Kun says, and the notes float over to Mark and Donghyuck with another flick of the wrist. "And these are notes for your professors, to excuse you should you be running late after your check-ups." The corner of Kun's mouth quirks up then, the first hint of a smile Mark's seen since he'd first stepped into the room. "That's about all I can do for now though, so you're both free to go after this. Do either of you have any further questions?"

Mark sighs, shaking his head as he takes the note in hand. "No, sir."

"Will I still be cleared for Quidditch practice?" Donghyuck asks, brows furrowed in worry at the prospect of letting his team down. His fingers clench tightly around the note, edges crumpling under the pressure. "Some of our practices are scheduled in the morning, and as captain, I can't afford to miss them."

Kun nods. "I don't see why not, although it might be a little harder to concentrate while you get used to Mark’s presence in your head. Physically though, there should be no problems, and these check-ups shouldn't last for more than half an hour, so you needn't worry about time."

When neither of the boys say anything more, Kun claps once in finality, and then gets up, a small, friendly smile on his face as he ushers the boys out of the room so they could carry on with the rest of their morning. "Well then, I guess that's it. Feel free to drop by if either of you feel anything changing, or if these headaches start to get worse."

He clamps a hand down on Mark's shoulder just as he steps past the threshold, making him pause. Donghyuck doesn't even spare him a second glance after he'd thanked Kun for their help, and Mark's eyes trail after him for a moment as his footsteps echo down the hall, before turning his attention back to Kun.

"Especially for you, Mark," Kun says, voice lowering. "I don't know what could be causing these symptoms, but if you have any idea, _anything_ at all that might be making it worse, please let me know, okay?"

Mark searches his face for a second, wondering at the worry etched into the lines of his concerned expression before he nods.

"Of course."

☾ ☼ ☽

"Donghyuck," Mark calls out, jogging up the empty hallway to catch up to Donghyuck's quick strides. "Hey! Donghyuck, wait up."

Mark reaches out to grab at Donghyuck's arm, tugging him back to get him to look at him.

— _ignore him ignore him doesn't deserve_ —

Mark frowns. "We need to talk about this, Hyuck—"

"No," Donghyuck cuts him off, glaring him so fiercely that Mark takes a step back, hand dropping limply by his side. "You do _not_ get to call me that anymore. You lost that right a long time ago, Mark. Don't forget that."

"Right," Mark says, voice clipped. He swallows thickly, eyes averting to the side. "Momentary lapse in judgment, sorry. I won't be forgetting that again." He looks back up, meeting Donghyuck's steely gaze as he continues. "But seriously, we really do need to talk about this."

"What's there to talk about?" Donghyuck grits out, arms coming up to cross against his chest. "I have you stuck in my fucking head."

 _There's nothing more to say_ , Donghyuck finishes in his head.

"Don't do that," Mark says. "Don't try to talk through the bond, it's—" He frowns then, as Donghyuck's lips start to twist up in a derisive smile. "It's weird," he finishes lamely.

"What's wrong?" Donghyuck grins, but it's sharp, dangerous as he takes a step closer to Mark. "Don't like the idea of me in your head, hm? I can't even imagine how difficult it's going to be for you, now that you have nothing to hide behind. No more secrets, not anymore," he snorts, like he finds this all to be particularly funny, a little inside joke that only he is privy to. "Not between _us_."

Mark recoils at that, a sharp intake of breath as he realizes the full gravity of their situation. Donghyuck's right, as much as Mark would hate to admit it, and he knows he has to tread lightly with his thoughts from now on. He can't allow himself to think about the past, what happened between them, and everything that led up to—

"No more secrets," Mark concedes, fists clenched by his side as he straightens his back. He smiles back at Donghyuck, a polite little thing that they both know is horribly fake—Mark's Head Boy smile, the picture-perfect image of the pureblood heir that he was always raised to be. "It goes both ways though, of course. This bond is a two-way street, after all."

He sees Donghyuck falter for a second, expression shuttering before turning carefully neutral. Cold, as it always is when he looks at Mark these days.

"Of course," Donghyuck says, voice tight. "Now, will that be all, Head Boy? I have practice to get to, and I'm already late enough as it is."

Mark studies him for a second, Donghyuck unflinchingly holding his gaze, before he nods.

"Not a word of this to anyone, Donghyuck," Mark says, tone leaving no room for argument as he moves to walk past him, pausing for just a moment as their shoulders brush at the proximity. Mark keeps his gaze focused pointedly ahead as he says, "We keep this between ourselves until we can sort this out."

Donghyuck scoffs.

_Obviously._

Mark winces as he hears Donghyuck's voice reverberate inside his head, but he doesn't let anything else give away the fact that he'd heard him, feet moving once more with the intent of heading back down into the Slytherin dungeons.

He doesn't look back to see if Donghyuck had moved, doesn't let himself wonder if Donghyuck had needed a moment to collect himself, just as he did when the coast was clear.

**Notes for the Chapter:**

> [cc](https://curiouscat.me/dhyuckiees) | [twitter](https://twitter.com/dhyuckIees)
> 
> up next: quidditch (but not really), more of mark and his headache, and meeting the aurors hehe


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